This is a double-blind, randomized, multicenter trial for the prevention of CMV end-organ disease in HIV-infected patients with CD4+ lymphocyte counts <100 cells/fl. Patients will be randomized to BW 256U87, acyclovir, or low-dose acyclovir. All groups will also take matching placebos. The two acyclovir control arms will provide suppressive therapy for Herpes simplex infections and will allow us to investigate possible dose-dependent effect on survival.